At present, radio communication systems which are compliant with LTE (Long Term Evolution), which is a standard developed by the Third Generation Partnership Project (3GPP), have been introduced. Moreover, as a fourth generation standard for radio communication systems, LTE-Advanced is being studied. In radio communication systems compliant with LTE or LTE-Advanced, frequency-division duplex (FDD) or time-division duplex (TDD) may be employed.
In radio communication systems compliant with LTE, FDD is typically employed. TDD has several advantages over FDD. For example, in FDD, it is necessary to provide a pair of an uplink frequency band and a downlink frequency band, while, in TDD, it is necessary to provide a single frequency band. Also, in FDD, the ratio of uplink communication resources and downlink communication resources is fixed, while, in TDD, the ratio of uplink communication resources and downlink communication resources is variable. Specifically, in TDD, the ratio of uplink communication resources and downlink communication resources can be changed by changing the link direction configuration of each sub-frame in a radio frame. Because of such advantages, it is expected that TDD will be increasingly employed in radio communication systems compliant with LTE or LTE-Advanced. Therefore, various techniques related to LTE TDD have been proposed.
For example, Patent Literature 1 discloses a technique of shifting the boundary between a downlink sub-frame and an uplink sub-frame, and communicating with another Home NodeB using a sub-frame between the boundaries before and after the shifting, thereby achieving radio communication between Home eNodeBs.